Four aspects of muscle function are to be investigated: 1) During neuromuscular transmission, the membrane bound vesicles empty their contents of transmitter. The fate of the vesicular membrane after emptying is to be examined. In particular, the question is whether or not the membrane is incorporated into the membrane of the nerve terminal. 2) The ionic specificity of the channels in the end plate membrane through which Na ion moves during the active phase of the end plate potential is to be examined. The effects of replacement of Na ion in the bath fluid by organic cations of varying size should give information as to the size of the Na ion channel. The results will be compared with those for the Na ion channel which opens during the rising phase of the action potential. 3) Various biochemical and contractile properties of muscle have been shown to be transformed by changing the innervation from fast to slow or vice versa (cross union experiments). The mechanism of this tranformation is to be investigated. Several approaches will be used to determine whether the transformation is based on extensive formation of new muscle fibers, or whether the properties of the original muscle fibers are altered following the new innervation. 4) The role of the membrane potential and of various divalent cations in the control of cytoplasmic streaming in Chaos and Amoeba will be investigated with microelectrode techniques.